[vsnet-alert 18859] Possible flare star 1.3' from ASASSN-15mt

[Denis Denisenko]

Following the discovery report of this possible dwarf nova in Cygnus
by ASAS-SN (ATel #7809) and [vsnet-alert 18856, 18857] I have checked
digitized Palomar plates and found a possible new variable 77" East of
ASASSN-15mt. This is likely a flaring red dwarf of UV Ceti type.

Animation of 1953, 1988 and 1990 POSS Blue plates centered at ASASSN-15mt:
http://hea.iki.rssi.ru/~denis/ASASSN-15mt-newVar-anim-Blue.gif
(200x200" FOV at 2x zoom)
The new variable is marked as New Var to the left from ASASSN-15mt.

The star has B2=20.01 in USNO-B1.0 measured from 1988-06-20 plate, but
it has brightened at least to 18.8m on the 1990-07-21 POSS-II Blue
plate. Taking into account the long exposure time of POSS-II plates
(60 minutes on 1990-07-21) and the short duration of UV Ceti flares
(typically a minute), the real range of variability may be much larger
(up to 15m).

The variable was submitted to AAVSO VSX with the temporary name DDE 40
and the following IDs:
USNO-B1.0 1405-0308849 = KIC 12056056 = 2MASS J19124371+5034398 = WISE
J191243.68+503439.7
J-K and W1-W2 colors are typical for red dwarfs, and URAT1 gives a
proper motion of (5.5, -19.4) mas/yr.

Finder chart centered at DDE 40: http://hea.iki.rssi.ru/~denis/DDE40-BRIR5x5.jpg

Please take a look at this star if you're doing time-resolved
photometry of ASASSN-15mt.

Denis Denisenko
Sternberg Astronomical Institute of Moscow State University